This invention relates generally to a fastener unit including an axially compressible spring washer member and more particularly concerns such a unit which has increased effectiveness in resisting retrograde movement of the unit.
Fastener units are currently available which include a spring washer member of a generally dished configuration secured to a bearing surface on either a nut member or a bolt member. The spring washer increases the static friction between the mating thread convolutions upon compression and thus provides resistance to free retrograde motion of the fastener unit. Other prior art units also rely on the biting tooth contact which may be provided on a spring washer member to provide increased resistance to retrograde motion of the fastener unit.
However, there are certain environments which inherently include high vibrations or other elements tending to loosen the tension in the joint. It is accordingly an object of the present invention to provide a fastener unit which has increased resistance to unauthorized retrograde motion of the fastener unit.
It is a more specific object of the invention to provide a nut and spring washer preassembled unit which requires that the washer be moved in a translational direction in order for the nut member to be loosened.
Another object of the invention is to provide a spring locking unit which will provide a visual indication that the unit has been tightened to a predetermined amount.
In addition to the foregoing objects and advantages, it should be understood that the present invention contemplates the provision of a rotary fastener member, such as a nut, which is provided with a threaded bore and a generally annular shank extending a short distance from one clamping surface upon which a dish shaped spring washer is mounted in a preassembled fashion. The axis of the threaded bore is displaced laterally from the axis of the annular mounting shank so that as the nut member is rotated about the threaded bore axis a crank arm is produced forcing the washer member to include at least an element of translational movement over the associated workpiece. This element of translational movement increases the frictional force which must be overcome if the rotary fastener member is to move in a retrograde direction. This translational movement friction, coupled with the spring tension and perhaps biting teeth in the outer periphery of the washer provides a unit with greatly increased locking efficiency.